This invention is related to the composition of an elastomeric triblock copolymer, and, additionally, to the use of such an elastomeric copolymer to prepare dip-formed articles.
Thin-walled, extensible articles such as gloves, condoms, and other medical products have long been made from natural rubber. In normal production, such articles are formed from natural rubber latex, a naturally occurring emulsion of rubber and water, with added stabilizing agents and vulcanizing chemicals. A form of the appropriate shape, previously coated with a coagulating solution in some cases, is dipped into the latex mixture once or several times to build up a layer of the desired thickness. The water is allowed to evaporate, leaving a solid rubber film. The film must be vulcanized to provide adequate mechanical and physical properties.
Natural rubber has many advantages in these applications, being strong and highly elastic and having good "tactility" or feeling to the user. The good tactility is believed to be a result of its low deformation stress at 10-500 percent elongations and high elastic recovery from these elongations. Natural rubber has the shortcoming that the resulting rubber film devices are sometimes prone to having "pinholes" therethrough, often on the order of micrometers in diameter. The pinholes are probably due to minute impurities in the natural latex which are difficult to filter out, and to the fact that the process converts a stable emulsion to a film by coagulating chemicals or heat. Natural rubber is also susceptible to rapid attack by ozone which causes scission cracking, as well as to oxidative attack during storage which causes cracking and destroys the physical integrity of the product. Even with these problems, for many applications the pinholes do not prevent the rubber article from having utility, and latex gloves, condoms, and other products are widely used. However, the presence of the pinholes is unacceptable in other applications, as for example where there is any possibility of the presence of the AIDS virus. Natural rubber is also not hypoallergenic due to the residual surfactants, vulcanizing agents, stabilizing agents, antioxidants, or protein materials in the rubber. Persons who are particularly susceptible to irritation or sensitization, or use the rubber products for extended periods of time may experience allergic reactions.
Various types of synthetic elastomeric polymer products have been developed for use in thin articles produced by dip forming. Synthetic rubber compositions can be dissolved in solvents to form a true solution, so that pinholes are much less likely to be present. Available synthetic rubber compositions have various other shortcomings, including unacceptable tactility. While each may meet some of the requirements, the known synthetic compositions do not have the required combination of strength, tactility, resistance to environmental damage, and hypoallergenicity required for many products such as examination and surgical gloves, condoms, and other medical products that are to come into contact with the human body. Several synthetic elastomeric systems have provided strength and tactility, but none has solved the problems related to environmental damage and hypoallergenicity required for surgical gloves and condoms.
There is therefore a need for an improved elastomeric material for use in thin, dip-formed articles used in a wide variety of applications, particularly medical applications. Such a material must have the required properties of strength and elastic elongation. It also must be pinhole free when the article is formed and used, resistant to immediate environmental damage occurring during storage or use, and hypoallergenic. The present invention fulfills this need, and further provides related advantages.